(function(doc, win) {
    // 分辨率Resolution适配
    var docEl = doc.documentElement,
      resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
      recalc = function() {
        var clientWidth = docEl.clientWidth;
        if (!clientWidth) return;
        docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
      };
    // Abort if browser does not support addEventListener
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener('DOMContentLoaded', recalc, false);
   
    // 一物理像素在不同屏幕的显示效果不一样。要根据devicePixelRatio来修改meta标签的scale,要注释上面的meta标签
    (function() {
    //   return;
      var dpr = scale = 1;
      var isIPhone = win.navigator.appVersion.match(/iphone/gi);
      var devicePixelRatio = win.devicePixelRatio;
      if (isIPhone) {
        // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
        if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
          dpr = 3;
        } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)) {
          dpr = 2;
        } else {
          dpr = 1;
        }
      } else {
        // 其他设备下，仍旧使用1倍的方案
        dpr = 1;
      }
      scale = 1 / dpr;
   
      //
      var metaEl = "";
      metaEl = doc.createElement('meta');
      metaEl.setAttribute('name', 'viewport');
      metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
      if (docEl.firstElementChild) {
        docEl.firstElementChild.appendChild(metaEl);
      } else {
        var wrap = doc.createElement('div');
        wrap.appendChild(metaEl);
        doc.write(wrap.innerHTML);
      }
    })();
   
  })(document, window);